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Rule 6.4.7 Exhibit G- Water Information <br />11. Please provide the most current SWSP issued by the Office of the State Engineer. <br />12. The operator states that seasonal baseline data is not necessary, and that only a few ground water <br />levels will be obtained. The Division believes that the seasonal high groundwater elevation and the <br />seasonal low are critical readings regarding the impacts from the groundwater mounding and <br />shadowing effects from the liners. Please commit to obtaining baseline data for the seasonal high <br />and low ground water elevations. <br />13. The operator has located 3 of the 5 monitoring locations on Exhibit G. Please locate the 2 other <br />monitoring locations (the east and southwest ponds) on Exhibit G. <br />14, The applicant proposes a "trigger point" of four (4) feet beyond the baseline elevation for <br />determining when mitigation measures will be implemented on the eastem lakes. Please discuss <br />how this criteria was determined, and whether this criteria is adequate to ensure no adverse impacts <br />to the eastern lakes. <br />15, According to Exhibit G, it appears that most if not all of the site lies within the 100-yeaz floodplain <br />(and possibly within the 1Q, 25, & 50-yeaz floodplains) of St. Vrain Creek. In the event of a <br />significant flood event (10-year flood or greater) it is likely that the existing pits and/or reclaimed <br />lakes will be captured by St. Vrain Creek. Accordingly, the Division requests that the applicant <br />provide the flood elevations(s) to be expected under a "worst case" flooding scenario and specific <br />mitigation measures that will be implemented to minimize the potential for any offsite impacts. <br />Mitigation measures might include mining dry pit slopes at a maximum of 1:1, installation of flood <br />control spillways within the reclaimed lakes, installation of drainage pipes within the internal berms <br />separating pits and/or armoring reclaimed pit slopes in close proximity to St. Vrain Creek with <br />erosion control riprap. If flood mitigation plans aze to be prepazed, they must specifically address <br />the potential for erosion of the lateral berms between the pits and the gas/oil pipeline both during <br />mining and following reclamation. <br />16. Please quantify the velocity and volume of flows expected on site from a 100-yeaz flood event, as <br />well as the elevation of the 100-year base flood event and its relation to the elevation of any <br />proposed spillways and lake shore embankment. Also, please quantify or characterize the expected <br />groundwater surface between the stream channel and the adjacent floodplain under such event. <br />17. Please quantify the velocity and volume of flow expected as well as magnitude of flood event <br />required to produce a "bankfull" event in the adjacent reach of the St. Vrain River. Also, please <br />quantify or chazacterize the expected groundwater surface between the stream channel and the <br />adjacent floodplain under such event. <br />18. Please provide a representative cross sectional diagram for each of the three (3) mined lakes which <br />adequately depicts the features of the alluvial aquifer with the affected and surrounding azeas. The <br />cross sectional diagram should be drawn to scale and provide the following information; <br />o Existing reclaimed excavations(s) and high lake water elevation <br />o Groundwater (piezometric) surface <br />3 <br />